Carlina is an interferometer working in the visible wavelength and configured like a diluted version of the Arecibo radiotelescope. Above the diluted primary mirror, made of fixed co-spherical segments, a helium balloon, or cables suspended between two mountains, carries a gondola containing the focal optics, and detector. We are building at Observatoire de Haute-Provence a technical demonstrator of this diluted telescope. Acquiring stellar fringes is the main difficulty for astronomical interferometers. Because there is no delay-lines, Carlina will easily work with hundreds of mirrors and should be more sensitive than regular interferometers. We present the servo-loop system and the optical design for coherencing the spaced primary mirrors of the OHP prototype interferometer using a supercontinum Laser source. This is an important step that demonstrates the feasibility of building a diluted telescope using cables strained between cliffs or under a balloon. We conclude that Carlina like the LBT comes from a new family of telescopes called the Diluted Telescopes. We propose to build in the next 10 years a 100m aperture scientific demonstrator that we will call the Large Diluted Telescope (LDT). Such interferometers will open new fields of research in astrophysics by imaging the surfaces of supergiant stars, gravitational microlensing, AGN, Hot Jupiters, etc. Considering its expected specifications, a LDT will operate in complementarity with ELTs and very long baseline interferometers.